Belt device, fixing device, and image forming apparatus

ABSTRACT

A belt device includes an endless belt and a rotary driver contacting an outer circumferential surface of the belt to drive and rotate the belt. An opposed belt support is disposed opposite the rotary driver and in contact with an inner circumferential surface of the belt. A rotary belt support is disposed opposite the rotary driver via the opposed belt support and in contact with the inner circumferential surface of the belt. A belt support holder holds the opposed belt support and the rotary belt support to retain a predetermined interval between the opposed belt support and the rotary belt support. A biasing assembly presses against the belt support holder to move the opposed belt support and the rotary belt support collectively with respect to the rotary driver and bias the opposed belt support against the rotary driver.

CROSS-REFERENCE TO RELATED APPLICATION

This patent application is based on and claims priority pursuant to 35U.S.C. §119 to Japanese Patent Application No. 2014-203850, filed onOct. 2, 2014, in the Japanese Patent Office, the entire disclosure ofwhich is hereby incorporated by reference herein.

BACKGROUND

1. Technical Field

Exemplary aspects of the present disclosure relate to a belt device, afixing device, and an image forming apparatus, and more particularly, toa belt device incorporating an endless belt, a fixing device for fixinga toner image on a recording medium, and an image forming apparatusincorporating the fixing device.

2. Description of the Background

Related-art image forming apparatuses, such as copiers, facsimilemachines, printers, or multifunction printers having two or more ofcopying, printing, scanning, facsimile, plotter, and other functions,typically form an image on a recording medium according to image data.Thus, for example, a charger uniformly charges a surface of aphotoconductor; an optical writer emits a light beam onto the chargedsurface of the photoconductor to form an electrostatic latent image onthe photoconductor according to the image data; a developing devicesupplies toner to the electrostatic latent image formed on thephotoconductor to render the electrostatic latent image visible as atoner image; the toner image is directly transferred from thephotoconductor onto a recording medium or is indirectly transferred fromthe photoconductor onto a recording medium via an intermediate transferbelt; finally, a fixing device applies heat and pressure to therecording medium bearing the toner image to fix the toner image on therecording medium, thus forming the image on the recording medium.

Such fixing device may include a belt device that includes an endlessbelt, such as a fixing belt and a fixing film, heated by a heater and arotary driver, such as a pressure roller and a pressure belt, pressedagainst the endless belt to form a fixing nip therebetween through whicha recording medium bearing a toner image is conveyed. As the recordingmedium bearing the toner image is conveyed through the fixing nip, theendless belt and the rotary driver apply heat and pressure to therecording medium, melting and fixing the toner image on the recordingmedium.

SUMMARY

This specification describes below an improved belt device. In oneexemplary embodiment, the belt device includes an endless belt and arotary driver contacting an outer circumferential surface of the belt todrive and rotate the belt. An opposed belt support is disposed oppositethe rotary driver and in contact with an inner circumferential surfaceof the belt. A rotary belt support is disposed opposite the rotarydriver via the opposed belt support and in contact with the innercircumferential surface of the belt. A belt support holder holds theopposed belt support and the rotary belt support to retain apredetermined interval between the opposed belt support and the rotarybelt support. A biasing assembly presses against the belt support holderto move the opposed belt support and the rotary belt supportcollectively with respect to the rotary driver and bias the opposed beltsupport against the rotary driver.

This specification further describes an improved fixing device. In oneexemplary embodiment, the fixing device includes an endless belt and arotary driver contacting an outer circumferential surface of the belt todrive and rotate the belt. An opposed belt support is disposed oppositethe rotary driver and in contact with an inner circumferential surfaceof the belt. A rotary belt support is disposed opposite the rotarydriver via the opposed belt support and in contact with the innercircumferential surface of the belt. A heater heats the belt. A beltsupport holder holds the opposed belt support and the rotary beltsupport to retain a predetermined interval between the opposed beltsupport and the rotary belt support. A biasing assembly presses againstthe belt support holder to move the opposed belt support and the rotarybelt support collectively with respect to the rotary driver and bias theopposed belt support against the rotary driver.

This specification further describes an improved image formingapparatus. In one exemplary embodiment, the image forming apparatusincludes an image forming device to form a toner image and a fixingdevice disposed downstream from the image forming device in a recordingmedium conveyance direction to fix the toner image on a recordingmedium. The fixing device includes an endless belt and a rotary drivercontacting an outer circumferential surface of the belt to drive androtate the belt. An opposed belt support is disposed opposite the rotarydriver and in contact with an inner circumferential surface of the belt.A rotary belt support is disposed opposite the rotary driver via theopposed belt support and in contact with the inner circumferentialsurface of the belt. A heater heats the belt. A belt support holderholds the opposed belt support and the rotary belt support to retain apredetermined interval between the opposed belt support and the rotarybelt support. A biasing assembly presses against the belt support holderto move the opposed belt support and the rotary belt supportcollectively with respect to the rotary driver and bias the opposed beltsupport against the rotary driver.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the disclosure and the many attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 is a schematic vertical sectional view of an image formingapparatus according to an exemplary embodiment of the presentdisclosure;

FIG. 2 is a schematic vertical sectional view of a fixing deviceaccording to a first exemplary embodiment of the present disclosure,which is installed in the image forming apparatus shown in FIG. 1;

FIG. 3 is a vertical sectional view of the fixing device shown in FIG. 2illustrating a holding mechanism and a driving force transmitterincorporated therein;

FIG. 4 is a schematic vertical sectional view of a comparative fixingdevice;

FIG. 5 is a schematic vertical sectional view of another comparativefixing device;

FIG. 6 is a schematic vertical sectional view of the comparative fixingdevice shown in FIG. 5 illustrating a holding mechanism and a drivingforce transmitter incorporated therein;

FIG. 7 is a schematic vertical sectional view of a fixing deviceaccording to a second exemplary embodiment of the present disclosure;

FIG. 8 is a perspective view of a temperature detector holderincorporated in the fixing device shown in FIG. 7;

FIG. 9 is a schematic vertical sectional view of the fixing device shownin FIG. 7 illustrating a holding mechanism and a driving forcetransmitter incorporated therein;

FIG. 10 is a schematic vertical sectional view of a fixing deviceaccording to a third exemplary embodiment of the present disclosureillustrating a holding mechanism and a driving force transmitterincorporated therein;

FIG. 11 is a perspective view of a heating roller holding portion and afixing pad holding portion incorporated in the fixing device shown inFIG. 10 before assembling;

FIG. 12 is a sectional view of the heating roller holding portion andthe fixing pad holding portion shown in FIG. 11 after assembling;

FIG. 13A is a sectional view of the heating roller holding portion andthe fixing pad holding portion shown in FIG. 12 before movement;

FIG. 13B is a sectional view of the heating roller holding portion andthe fixing pad holding portion shown in FIG. 12 after movement;

FIG. 14 is a graph showing a relation between a fixing nip length andfixing nip pressure of the fixing devices shown in FIGS. 9 and 10;

FIG. 15 is a schematic vertical sectional view of a fixing deviceaccording to a fourth exemplary embodiment of the present disclosureillustrating a holding mechanism and a driving force transmitterincorporated therein;

FIG. 16 is a schematic vertical sectional view of a fixing deviceaccording to a fifth exemplary embodiment of the present disclosureillustrating a holding mechanism and a driving force transmitterincorporated therein;

FIG. 17 is a schematic vertical sectional view of the fixing deviceshown in FIG. 16 illustrating a plurality of gears incorporated therein;and

FIG. 18 is a schematic vertical sectional view of the fixing deviceshown in FIG. 15 illustrating a plurality of gears incorporated therein.

DETAILED DESCRIPTION OF THE DISCLOSURE

In describing exemplary embodiments illustrated in the drawings,specific terminology is employed for the sake of clarity. However, thedisclosure of this specification is not intended to be limited to thespecific terminology so selected and it is to be understood that eachspecific element includes all technical equivalents that operate in asimilar manner and achieve a similar result.

Referring now to the drawings, wherein like reference numerals designateidentical or corresponding parts throughout the several views, inparticular to FIG. 1, an image forming apparatus 1 according to anexemplary embodiment of the present disclosure is explained.

It is to be noted that, in the drawings for explaining exemplaryembodiments of this disclosure, identical reference numerals areassigned, as long as discrimination is possible, to components such asmembers and component parts having an identical function or shape, thusomitting description thereof once it is provided.

FIG. 1 is a schematic vertical sectional view of the image formingapparatus 1. The image forming apparatus 1 may be a copier, a facsimilemachine, a printer, a multifunction peripheral or a multifunctionprinter (MFP) having at least one of copying, printing, scanning,facsimile, and plotter functions, or the like. According to thisexemplary embodiment, the image forming apparatus 1 is a color printerthat forms color and monochrome toner images on recording media byelectrophotography. Alternatively, the image forming apparatus may be amonochrome printer that forms a monochrome toner image on a recordingmedium.

It is to be noted that, in the drawings for explaining exemplaryembodiments of this disclosure, identical reference numerals areassigned as long as discrimination is possible to components such asmembers and component parts having an identical function or shape, thusomitting description thereof once it is provided.

With reference to FIG. 1, a description is provided of a construction ofthe image forming apparatus 1.

Four process units 2Y, 2M, 2C, and 2Y serving as an image forming deviceare located in a center portion of the image forming apparatus 1.Although the process units 2Y, 2M, 2C, and 2K contain developers indifferent colors, that is, yellow, magenta, cyan, and blackcorresponding to color separation components of a color image, (e.g.,yellow, magenta, cyan, and black toners), respectively, they have anidentical structure. For example, each of the process units 2Y, 2M, 2C,and 2K includes a photoconductor serving as an image bearer or a latentimage bearer that bears an electrostatic latent image and a resultanttoner image; a charging device serving as a charger that charges anouter circumferential surface of the photoconductor; a developing devicethat supplies the developer (e.g., toner) to the electrostatic latentimage formed on the outer circumferential surface of the photoconductor,thus visualizing the electrostatic latent image as a toner image; and acleaning device serving as a cleaner that cleans the outercircumferential surface of the photoconductor. For example, thedeveloper includes toner containing oily silica, that is, silicacontaining oil, as an additive.

Each of the four process units 2Y, 2M, 2C, and 2K is removably installedin the image forming apparatus 1. As a user lifts and pivots an uppercover 3 disposed atop the image forming apparatus 1 as illustrated in along and short dashed line in FIG. 1, the user picks up and removes eachof the process units 2Y, 2M, 2C, and 2K from the image forming apparatus1 and places and installs each of the process units 2Y, 2M, 2C, and 2Kinside the image forming apparatus 1.

Above the process units 2Y, 2M, 2C, and 2K is an exposure device 4 thatexposes the outer circumferential surface of the respectivephotoconductors with laser beams. The exposure device 4 is attached tothe upper cover 3. Hence, as the user lifts the upper cover 3, theexposure device 4 is retracted from a space above the process units 2Y,2M, 2C, and 2K together with the upper cover 3. Thus, the exposuredevice 4 facilitates removal and installation of the process units 2Y,2M, 2C, and 2K.

The image forming apparatus 1 further includes a sheet feeder 5 servingas a recording medium supply that supplies a sheet serving as arecording medium to the process units 2Y, 2M, 2C, and 2K; a transferdevice 6 serving as a transferor that transfers a toner image formed onthe photoconductor onto the sheet; a fixing device 7 that fixes thetoner image on the sheet; and an output roller pair 8 serving as arecording medium ejector that ejects the sheet bearing the fixed tonerimage onto an outside of the image forming apparatus 1.

For example, the transfer device 6 includes an endless intermediatetransfer belt 9, four primary transfer rollers 10 serving as primarytransferors, and a secondary transfer roller 11 serving as a secondarytransferor. The four primary transfer rollers 10 are pressed against thefour photoconductors of the four process units 2Y, 2M, 2C, and 2K,respectively, via the intermediate transfer belt 9, forming four primarytransfer nips between the intermediate transfer belt 9 and thephotoconductors. The secondary transfer roller 11 is pressed against oneof a plurality of rollers across which the intermediate transfer belt 9is stretched taut via the intermediate transfer belt 9, forming asecondary transfer nip between the secondary transfer roller 11 and theintermediate transfer belt 9.

The secondary transfer roller 11 is attached to a front cover 12 that isopened and closed by the user. As the user pivots and opens the frontcover 12 toward the user, the secondary transfer roller 11 separatesfrom the intermediate transfer belt 9 as illustrated in a long and shortdashed line in FIG. 1. Thus, the secondary transfer roller 11facilitates removal of the sheet jammed at the secondary transfer nip.

With reference to FIG. 1, a description is provided of an image formingoperation performed by the image forming apparatus 1 having theconstruction described above to form a color toner image on a sheet.

As the image forming apparatus 1 receives a print job, the process units2Y, 2M, 2C, and 2K form yellow, magenta, cyan, and black toner images,respectively. For example, in each of the process units 2Y, 2M, 2C, and2K, the photoconductor is driven and rotated and the charging deviceuniformly charges the outer circumferential surface of thephotoconductor at a predetermined polarity. The exposure device 4exposes the outer circumferential surface of the photoconductor with alaser beam, forming an electrostatic latent image on the photoconductoraccording to monochrome image data, that is, yellow, magenta, cyan, andblack image data created by decomposing desired color image data. Thedeveloping device supplies toner to the electrostatic latent imageformed on the photoconductor, developing or visualizing theelectrostatic latent image into a toner image, that is, yellow, magenta,cyan, and black toner images.

The yellow, magenta, cyan, and black toner images are primarilytransferred from the photoconductors onto the intermediate transfer belt9 successively at the primary transfer nips such that the yellow,magenta, cyan, and black toner images are superimposed on a sameposition on the intermediate transfer belt 9. The cleaning deviceremoves residual toner failed to be transferred onto the intermediatetransfer belt 9 and therefore remaining on the photoconductor therefrom.The yellow, magenta, cyan, and black toner images superimposed on theintermediate transfer belt 9 are secondarily transferred onto the sheetconveyed from the sheet feeder 5 at the secondary transfer nipcollectively. Thus, a color toner image is formed on the sheet. Thesheet bearing the color toner image, after passing through the secondarytransfer nip, is conveyed to the fixing device 7 that fixes the colortoner image on the sheet. Thereafter, the sheet bearing the fixed colortoner image is ejected by the output roller pair 8 onto the outside ofthe image forming apparatus 1.

The above describes the image forming operation of the image formingapparatus 1 to form the color toner image, that is, a full-color tonerimage, on the sheet. Alternatively, the image forming apparatus 1 mayform a monochrome toner image by using any one of the four process units2Y, 2M, 2C, and 2K or may form a bicolor or tricolor toner image byusing two or three of the process units 2Y, 2M, 2C, and 2K.

With reference to FIG. 2, a description is provided of a construction ofthe fixing device 7 according to a first exemplary embodiment that isincorporated in the image forming apparatus 1 described above.

FIG. 2 is a schematic vertical sectional view of a main section of thefixing device 7. As shown in FIG. 2, the fixing device 7 (e.g., a fuseror a fusing unit) includes a fixing belt 20, a pressure roller 21, afixing pad 22, a heating roller 23, a halogen heater 24, a plate spring25, and a fixing stay 26. The fixing belt 20 serves as an endless belt.The pressure roller 21 serves as a rotary driver that contacts an outercircumferential surface of the fixing belt 20 to drive and rotate thefixing belt 20. The fixing pad 22 serves as an opposed belt support thatis in contact with an inner circumferential surface of the fixing belt20 and is disposed opposite the pressure roller 21 via the fixing belt20. The heating roller 23 serves as a rotary belt support that is incontact with the inner circumferential surface of the fixing belt 20 andis disposed opposite the pressure roller 21 via the fixing pad 22. Theplate spring 25 serves as a tension applicator that exerts tension tothe fixing belt 20. The halogen heater 24 serves as a heat generator ora heater that heats the fixing belt 20 via the heating roller 23. Thefixing stay 26 serves as an opposed belt support holder that holds thefixing pad 22.

A detailed description is now given of a configuration of the fixingbelt 20.

The fixing belt 20 is looped over and supported by the fixing pad 22 andthe heating roller 23. The plate spring 25 disposed opposite the innercircumferential surface of the fixing belt 20 presses against the fixingbelt 20, exerting a predetermined tension to the fixing belt 20. Thefixing pad 22 presses against the pressure roller 21 via the fixing belt20 with predetermined pressure, forming a fixing nip N between thefixing belt 20 and the pressure roller 21.

A detailed description is now given of a configuration of the halogenheater 24.

The halogen heater 24 heats the heating roller 23 which in turn heatsthe fixing belt 20 so that the fixing belt 20 heats a sheet P as thesheet P is conveyed through the fixing nip N. According to thisexemplary embodiment, the halogen heater 24 is disposed inside theheating roller 23. Alternatively, the halogen heater 24 may be disposedopposite the outer circumferential surface of the fixing belt 20. Yetalternatively, a heat generator or a heater may be disposed opposite thefixing pad 22 to heat the fixing pad 22. The heat generator or theheater may be a halogen heater, an induction heater (IH) incorporatingan IH coil, a resistance heat generator, a carbon heater, or the like.The heat generator or the heater may be disposed inside the pressureroller 21 to heat the pressure roller 21. The heat generator or theheater may heat the heating roller 23 and the fixing pad 22 that have athermal capacity smaller than that of the pressure roller 21 to saveenergy.

The pressure roller 21 is driven and rotated in a rotation direction A.The heating roller 23 is driven and rotated in a rotation direction B.Accordingly, the fixing belt 20 is driven and rotated in a rotationdirection C while the fixing belt 20 slides over the fixing pad 22.Optionally, a slide sheet having a decreased friction coefficient may besandwiched between the fixing pad 22 and the fixing belt 20 tofacilitate sliding of the fixing belt 20 over the fixing pad 22.

With reference to FIG. 2, a description is provided of a fixingoperation performed by the fixing device 7.

As the image forming apparatus 1 depicted in FIG. 1 is powered on, thehalogen heater 24 is supplied with power and the pressure roller 21 andthe heating roller 23 are driven and rotated in the rotation directionsA and B, respectively. As the fixing belt 20 is driven and rotated bythe heating roller 23 heated by the halogen heater 24, the heatingroller 23 heats the fixing belt 20 which in turn heats the fixing nip N.

When the fixing nip N is heated to a predetermined fixing temperature,as a sheet P bearing an unfixed toner image T is conveyed through thefixing nip N in a sheet conveyance direction DP, the fixing belt 20 andthe pressure roller 21 melt toner of the toner image T, thus fixing thetoner image T on the sheet P under heat and pressure. Then, the sheet Pbearing the fixed toner image T is discharged from the fixing nip Nwhile being separated from the fixing belt 20.

A description is provided of a construction of a holding mechanism and adriving force transmitter of the fixing device 7 according to the firstexemplary embodiment.

The holding mechanism holds the pressure roller 21, the fixing pad 22,and the heating roller 23. The driving force transmitter transmits adriving force to the pressure roller 21 and the heating roller 23. FIG.3 is a vertical sectional view of the fixing device 7 according to thefirst exemplary embodiment illustrating the holding mechanism and thedriving force transmitter.

First, a description is provided of a construction of the driving forcetransmitter.

The driving force transmitter includes a pressure roller gear 30 mountedon one lateral end of the pressure roller 21 in an axial directionthereof; a heating roller gear 31 mounted on one lateral end of theheating roller 23 in an axial direction thereof; and two relay gears,that is, a first gear 32 meshing with the heating roller gear 31 and asecond gear 33 meshing with the pressure roller gear 30.

The second gear 33 also meshes with a driving gear located inside theimage forming apparatus 1. As a driving force generated by a drivingsource (e.g., a motor) is transmitted from the driving gear to thesecond gear 33, the driving force is transmitted from the second gear 33to the pressure roller gear 30. The driving force is also transmittedfrom the second gear 33 to the heating roller gear 31 through the firstgear 32. Thus, the driving force transmitted as described above drivesand rotates the pressure roller 21 and the heating roller 23.

Next, a description is provided of a construction of the holdingmechanism.

Both lateral ends of the pressure roller 21 in the axial directionthereof are rotatably mounted on a pair of platy frames 41 of the fixingdevice 7 through a pair of bearings 40, respectively. Each bearing 40 isinserted into and mounted in a pressure roller holding through-hole 41 aprovided in each frame 41. Thus, the pressure roller 21 is held by theframes 41 such that an axis of the pressure roller 21 is fixed relativeto the frames 41.

The fixing pad 22 and the heating roller 23 are movably held by theframes 41. For example, the fixing pad 22 and the heating roller 23 areheld by a belt support holder 42 movably attached to each frame 41. Thebelt support holder 42 is provided with a fixing pad holdingthrough-hole 42 a serving as an opposed belt support holdingthrough-hole and a heating roller holding through-hole 42 b serving as arotary belt support holding through-hole. The fixing stay 26 holding thefixing pad 22 is inserted into the fixing pad holding through-hole 42 a.An axial end 23 a, that is, each lateral end, of the heating roller 23in the axial direction thereof is rotatably inserted into the heatingroller holding through-hole 42 b.

The frame 41 includes a belt support holder holding through-hole 41 bthat movably holds the belt support holder 42. The belt support holder42 is inserted into the belt support holder holding through-hole 41 b.An edge of the belt support holder holding through-hole 41 b is insertedinto a pair of grooves 42 c of the belt support holder 42. The edge ofthe belt support holder holding through-hole 41 b inserted into thegrooves 42 c constitutes a guide 41 c. The guide 41 c extends linearlyin a direction D in which the belt support holder 42 moves closer to andaway from the pressure roller 21. Accordingly, as the belt supportholder 42 moves along the guide 41 c, the fixing pad 22 and the heatingroller 23 move linearly in a direction (e.g., the direction D) in whichthe fixing pad 22 and the heating roller 23 move closer to and away fromthe pressure roller 21.

The fixing device 7 further includes a pressure lever 43 and a pressurespring 44 serving as a biasing assembly that biases the fixing pad 22against the pressure roller 21. The pressure lever 43 is pivotable abouta shaft 45 disposed at one end of the pressure lever 43 and mounted onthe frame 41. The pressure spring 44 is anchored to an engagementportion 43 a (e.g., a hook) disposed at another end of the pressurelever 43 and an engagement portion 41 d of the frame 41 such that thepressure spring 44 is stretched across the engagement portions 43 a and41 d. The pressure spring 44 exerts a tensile force that presses thepressure lever 43 against a pressure lever side end 42 m serving as abiasing assembly side end, that is, a left end in FIG. 3, of the beltsupport holder 42 opposite a pressure roller side end 42 n serving as arotary driver side end disposed opposite the pressure roller 21. Thus,the pressure lever 43 moves the belt support holder 42 toward thepressure roller 21. Accordingly, the belt support holder 42 biases thefixing pad 22 against the pressure roller 21, positioning the fixing pad22 relative to the pressure roller 21 and forming the fixing nip Nbetween the fixing belt 20 and the pressure roller 21 as shown in FIG.2.

Since the pressure lever 43 presses against the belt support holder 42,if the heating roller holding through-hole 42 b is deformed by pressurefrom the pressure lever 43, the heating roller 23 may not rotatesmoothly, increasing a rotation torque of the heating roller 23. Toaddress this circumstance, a length E1 of the heating roller holdingthrough-hole 42 b in a pressurization direction of the pressure lever 43corresponding to the direction D is greater than a length E2 of theaxial end 23 a of the heating roller 23 in the pressurization directionof the pressure lever 43. Accordingly, even if the heating rollerholding through-hole 42 b is deformed by pressure from the pressurelever 43, the heating roller holding through-hole 42 b having the lengthE1 retains smooth rotation of the heating roller 23, preventing increaseof the rotation torque of the heating roller 23.

A description is provided of a construction of a comparative fixingdevice 7C 1.

FIG. 4 is a schematic vertical sectional view of the comparative fixingdevice 7C1. As shown in FIG. 4, the comparative fixing device 7C1includes a heating roller 100, a fixing pad 200 spaced apart from theheating roller 100, an endless fixing belt 300 looped over the heatingroller 100 and the fixing pad 200, and a pressure roller 400 pressedagainst the fixing pad 200 via the fixing belt 300 to form a fixing nipN between the fixing belt 300 and the pressure roller 400. The fixingbelt 300 is heated by a heater disposed inside the heating roller 100and is driven and rotated counterclockwise in FIG. 4 by the pressureroller 400 rotating clockwise in FIG. 4. As a sheet P bearing a tonerimage is conveyed through the fixing nip N, the fixing belt 300 and thepressure roller 400 fix the toner image on the sheet P under heat andpressure.

In order to form the fixing nip N, at least one of the pressure roller400 and the fixing pad 200 is pressed against another one of thepressure roller 400 and the fixing pad 200. If the pressure roller 400is configured to be movable with respect to the fixing pad 200, thepressure roller 400 serving as a driving roller that drives and rotatesthe fixing belt 300 may vary pressure exerted at the fixing nip N(hereinafter referred to as the fixing nip pressure) depending on adriving force transmitted to the pressure roller 400.

The driving force transmitted from a driving source to the pressureroller 400 through a gear train may generate a force that moves thepressure roller 400 closer to the fixing belt 300 or a force that movesthe pressure roller 400 away from the fixing belt 300 according to amesh position of the gear train. Accordingly, the fixing nip pressuremay increase or decrease. Additionally, the fixing nip pressure maychange as a torque generated at the gear train changes over time. Hence,if the pressure roller 400 is movable, the fixing nip pressure maychange, degrading stability of a fixing property of fixing the tonerimage on the sheet P properly under desired pressure.

If the gear train is disposed at one lateral end of the pressure roller400 in an axial direction thereof, one lateral end of the fixing belt300 in an axial direction thereof contacting the one lateral end of thepressure roller 400 may suffer from variation in the fixing nip pressurecaused by the driving force transmitted to the pressure roller 400.Accordingly, the fixing belt 300 may suffer from variation in the fixingnip pressure between one lateral end and another lateral end of thefixing belt 300 in the axial direction thereof. Consequently, the fixingbelt 300 may be skewed, resulting in breakage.

To address this circumstance, the fixing pad 200, instead of thepressure roller 400, may be configured to be movable. However, as thefixing pad 200 moves with respect to the stationary heating roller 100,an interval, that is, a distance, between the heating roller 100 and thefixing pad 200 may change, resulting in change in tension exerted to thefixing belt 300. As the tension exerted to the fixing belt 300increases, a driving torque to rotate the fixing belt 300 increases.Conversely, as the tension exerted to the fixing belt 300 decreases, thefixing belt 300 is susceptible to skew and resultant breakage.

The above-described problems resulting from change in the tensionexerted to the fixing belt 300 caused by change in the distance betweenthe heating roller 100 and the fixing pad 200 may also occur in a beltdevice having a construction similar to that of the comparative fixingdevice 7C 1.

A description is provided of operation and advantages of the fixingdevice 7 according to the first exemplary embodiment by comparing thefixing device 7 with another comparative fixing device 7C2.

First, a description is provided of a construction and disadvantages ofthe comparative fixing device 7C2.

FIG. 5 is a schematic vertical sectional view of a main section of thecomparative fixing device 7C2. Like the fixing device 7 according to thefirst exemplary embodiment shown in FIG. 2, the comparative fixingdevice 7C2 includes the fixing belt 20, the pressure roller 21, thefixing pad 22, the heating roller 23, the halogen heater 24, and thefixing stay 26. The pressure roller 21 and the heating roller 23 aredriven and rotated in the rotation directions A and B, respectively. Thefixing belt 20 is driven and rotated in the rotation direction C whilesliding over the fixing pad 22.

FIG. 6 is a schematic vertical sectional view of the comparative fixingdevice 7C2 illustrating a holding mechanism and a driving forcetransmitter. The driving force transmitter of the comparative fixingdevice 7C2 is equivalent to the driving force transmitter of the fixingdevice 7 shown in FIG. 3. For example, the driving force transmitter ofthe comparative fixing device 7C2 includes the pressure roller gear 30,the heating roller gear 31, and the two relay gears, that is, the firstgear 32 and the second gear 33. A driving force generated by a drivingsource (e.g., a motor) is transmitted to the pressure roller 21 and theheating roller 23 through those gears.

Conversely, the holding mechanism of the comparative fixing device 7C2is different from the holding mechanism of the fixing device 7 shown inFIG. 3 in a construction holding the fixing pad 22 and the heatingroller 23. The fixing pad 22 and the heating roller 23 are heldseparately such that the fixing pad 22 and the heating roller 23 aremovable independently, unlike the fixing pad 22 and the heating roller23 of the fixing device 7 that are held by the belt support holder 42such that the fixing pad 22 and the heating roller 23 are movabletogether.

For example, the fixing pad 22 is held by the fixing stay 26 held by astay holder 27. The stay holder 27 is inserted into a fixing pad holdingthrough-hole 41 e provided in each of the pair of frames 41 such thatthe stay holder 27 is movable in a direction G. Accordingly, the fixingpad 22 is movable in the direction G in which the fixing pad 22 movescloser to and away from the pressure roller 21.

Both lateral ends of the heating roller 23 in the axial directionthereof are rotatably mounted on the pair of platy frames 41 through apair of bearings 46, respectively. Each of the bearings 46 is insertedinto a heating roller holding through-hole 41 f provided in each of theframes 41 such that the bearing 46 is movable in a direction H.Accordingly, the heating roller 23 is also movable in the direction H inwhich the heating roller 23 moves closer to and away from the pressureroller 21.

A coil spring 28 serving as a tension applicator is interposed betweenthe fixing pad 22 and the heating roller 23. The coil spring 28 biasesagainst the heating roller 23 to separate the heating roller 23 from thefixing pad 22 so that the heating roller 23 and the fixing pad 22 exerttension to the fixing belt 20. Unlike the pressure lever 43 of thefixing device 7 shown in FIG. 3, the pressure lever 43 of thecomparative fixing device 7C2 presses against the fixing stay 26 that inturn presses the fixing pad 22 against the pressure roller 21 via thefixing belt 20.

The comparative fixing device 7C2 includes a holding mechanism to holdthe pressure roller 21 that is equivalent to the holding mechanism tohold the pressure roller 21 of the fixing device 7. Hence, the pressureroller 21 is held by the frames 41 such that the axis of the pressureroller 21 is fixed relative to the frames 41.

As a driving force generated by the driving source is transmitted to thecomparative fixing device 7C2, the second gear 33 rotatescounterclockwise in FIG. 6 to rotate the pressure roller gear 30clockwise and rotate the first gear 32 clockwise. The first gear 32rotates the heating roller gear 31 counterclockwise. Taking a forcereceived by the heating roller gear 31, the heating roller gear 31receives a driving force F from the first gear 32. The driving force Fdefines a force generated by teeth of the first gear 32 that pressagainst teeth of the heating roller gear 31 and exerted in a directioninclined by a pressure angle α from a perpendicular line perpendicularto a linear line defined by an axis of the heating roller gear 31 and anaxis of the first gear 32.

A parallel component f1 (hereinafter referred to as the heating rollermoving direction component f1) of the driving force F that is parallelto the direction H in which the heating roller 23 moves is exerted in adirection in which the heating roller 23 moves toward the pressureroller 21. The heating roller moving direction component f1 is exertedin a direction opposite a biasing direction in which the coil spring 28exerts a bias to the heating roller 23. Accordingly, the bias of thecoil spring 28 is decreased by the size of the heating roller movingdirection component f1, decreasing tension exerted to the fixing belt20. Since the driving force F is produced at one lateral end of theheating roller 23 in the axial direction thereof that mounts the heatingroller gear 31, the tension exerted to the fixing belt 20 is decreasedat one lateral end of the fixing belt 20 in an axial direction thereof.Accordingly, the tension exerted to the fixing belt 20 may vary betweenone lateral end and another lateral end of the fixing belt 20 in theaxial direction thereof, resulting in skew of the fixing belt 20.Consequently, the skewed fixing belt 20 may surmount a skew restrictorand may be damaged.

As a first method of eliminating variation in the tension exerted to thefixing belt 20, for example, the bias of the coil spring 28 anchored toone lateral end of the heating roller 23 in the axial direction thereofthat mounts the heating roller gear 31 may be increased to offset theheating roller moving direction component f1. However, since the heatingroller moving direction component f1 changes in accordance with changein torque of the heating roller gear 31 over time, even if the bias ofthe coil spring 28 is adjusted, variation in the tension exerted to thefixing belt 20 may not be overcome for an extended period of time.

As a second method of eliminating variation in the tension exerted tothe fixing belt 20, the axis of the heating roller 23 is fixed toprevent the heating roller 23 from being moved by the heating rollermoving direction component f1. However, this method may cause anotherproblem of changing an interval, that is, a distance, between theheating roller 23 and the fixing pad 22 as the fixing pad 22 moves. Theposition of the fixing pad 22 changes over time as the outer diameterand the rigidity of a surface rubber layer of the pressure roller 21change. Accordingly, as the position of the fixing pad 22 changes, theinterval between the heating roller 23 and the fixing pad 22 changes.Accordingly, the tension exerted to the fixing belt 20 changes. As thetension exerted to the fixing belt 20 increases, the driving torque torotate the fixing belt 20 increases, generating noise and stopping themotor. Conversely, as the tension exerted to the fixing belt 20decreases, the fixing belt 20 is susceptible to skew and resultantbreakage.

To address those problems, the fixing device 7 according to the firstexemplary embodiment shown in FIG. 3 includes the belt support holder 42that holds and moves the heating roller 23 and the fixing pad 22together while retaining the interval between the heating roller 23 andthe fixing pad 22. Thus, the belt support holder 42 prevents the tensionexerted to the fixing belt 20 from changing as the interval between theheating roller 23 and the fixing pad 22 changes.

As shown in FIG. 3, since the heating roller holding through-hole 42 bis greater than the axial end 23 a of the heating roller 23, an axis ofthe heating roller 23 is not fixed relative to the heating rollerholding through-hole 42 b. Accordingly, if the heating roller 23 movesinside the heating roller holding through-hole 42 b, the intervalbetween the heating roller 23 and the fixing pad 22 changes. However,the heating roller 23 is pressed against a fixing pad side edge 42 b 1,that is, a right edge in FIG. 3, of the heating roller holdingthrough-hole 42 b by two forces described below and positioned relativeto the fixing pad 22, retaining the predetermined interval between theheating roller 23 and the fixing pad 22.

A first force that presses the heating roller 23 against the fixing padside edge 42 b 1 of the heating roller holding through-hole 42 b is thetension exerted to the fixing belt 20. As shown in FIG. 2, the fixingbelt 20 looped over the heating roller 23 is exerted with tensions T1and T2. The heating roller 23 is exerted with a resultant force J of thetensions T1 and T2. The resultant force J is exerted in a direction inwhich the heating roller 23 moves toward the pressure roller 21.Accordingly, the resultant force J presses the heating roller 23 againstthe fixing pad side edge 42 b 1, that is, the right edge in FIG. 3, ofthe heating roller holding through-hole 42 b.

A second force is a driving force received by the heating roller gear 31from the first gear 32. As the second gear 33, the pressure roller gear30, the first gear 32, and the heating roller gear 31 arranged as shownin FIG. 3 rotate in rotation directions D33, D30, D32, and D31,respectively, the heating roller gear 31 receives the driving force Ffrom the first gear 32. The driving force F is exerted in a direction inwhich the heating roller 23 moves toward the pressure roller 21.Accordingly, the driving force F presses the heating roller 23 againstthe fixing pad side edge 42 b 1, that is, the right edge in FIG. 3, ofthe heating roller holding through-hole 42 b.

As described above, the heating roller 23 is pressed against the fixingpad side edge 42 b 1 of the heating roller holding through-hole 42 b bythe tension exerted to the fixing belt 20 and the driving force Ftransmitted from the first gear 32 through the heating roller gear 31and positioned relative to the fixing pad 22, retaining thepredetermined interval between the heating roller 23 and the fixing pad22 through the belt support holder 42. Accordingly, even if the positionof the fixing pad 22 changes as the outer diameter and the rigidity ofthe pressure roller 21 change, the heating roller 23 moves in accordancewith motion of the fixing pad 22, retaining the predetermined intervalbetween the heating roller 23 and the fixing pad 22. Consequently, thebelt support holder 42 prevents the tension exerted to the fixing belt20 from changing as the interval between the heating roller 23 and thefixing pad 22 changes, thus preventing various faults caused by changein the tension exerted to the fixing belt 20.

The pair of belt support holders 42 is constructed of identical parts toreduce variation in the position of the heating roller 23 and the fixingpad 22 between one lateral end and another lateral end of the fixingbelt 20 in the axial direction thereof. Thus, the belt support holder 42suppresses variation in the tension exerted to the fixing belt 20depending on variation in the position of the heating roller 23 and thefixing pad 22 in the axial direction of the fixing belt 20, thussuppressing skew of the fixing belt 20.

As described above, since the heating roller 23 is pressed against thefixing pad side edge 42 b 1 of the heating roller holding through-hole42 b as the heating roller gear 31 receives the driving force, the beltsupport holder 42 receives the bias exerted to the heating roller 23.Accordingly, the belt support holder 42 prevents the bias exerted to onelateral end of the heating roller 23 in the axial direction thereof fromchanging the tension exerted to the fixing belt 20, thus preventingvariation in the tension exerted to the fixing belt 20 and resultantskew of the fixing belt 20.

Alternatively, in order to prevent variation in the tension exerted tothe fixing belt 20, the heating roller 23 may be driven and rotated bythe fixing belt 20 without mounting the heating roller gear 31. In thiscase, the driving force is not transmitted to the heating roller 23through the second gear 33, the first gear 32, and the heating rollergear 31, preventing variation in the tension exerted to the fixing belt20.

However, since the motor drives and rotates the pressure roller 21 only,the fixing belt 20 may slip relative to the pressure roller 21. Toaddress this circumstance, the pressure roller 21 includes a gripportion disposed at each lateral end of the pressure roller 21 in theaxial direction thereof and constructed of a frictional silicone rubberlayer or the like that contacts the fixing belt 20 with an increasedfriction therebetween to grip the fixing belt 20. However, the gripportion is disposed outboard from a tube layer facilitating separationof the sheet P from the pressure roller 21 in the axial directionthereof, which constitutes a conveyance span on the pressure roller 21where the sheet P is conveyed, thus increasing the width of the pressureroller 21 in the axial direction thereof and upsizing the fixing device7.

To address this circumstance, the fixing device 7 according to thisexemplary embodiment includes the heating roller 23 driven and rotatedby the motor, preventing slippage of the fixing belt 20 without the gripportion disposed at each lateral end of the pressure roller 21 in theaxial direction thereof. Thus, the heating roller 23 rotates the fixingbelt 20 stably while downsizing the fixing device 7.

According to this exemplary embodiment, like the heating roller 23, thepressure roller 21 receives a driving force transmitted through a geartrain disposed at one lateral end of the pressure roller 21 in the axialdirection thereof. Accordingly, the pressure roller 21 is also exertedwith a bias as the pressure roller 21 receives the driving force at onelateral end of the pressure roller 21 in the axial direction thereof. Ifthe bias generated at one lateral end of the pressure roller 21 in theaxial direction thereof changes pressure exerted at the fixing nip N,the pressure exerted at the fixing nip N varies in a width direction ofthe fixing nip N parallel to the axial direction of the pressure roller21, resulting in skew of the fixing belt 20.

To address this circumstance, according to this exemplary embodiment,the axis of the pressure roller 21 is retained at a fixed positionconstantly. Accordingly, even if the pressure roller 21 receives thedriving force at one lateral end of the pressure roller 21 in the axialdirection thereof, the pressure roller 21 is not susceptible to the biasgenerated by the driving force. Consequently, variation in pressureexerted at the fixing nip N caused by the driving force exerted to thepressure roller 21 is prevented, thus preventing skew of the fixing belt20 precisely.

Table 1 below shows a result of an endurance test for comparingendurance of an image forming apparatus incorporating the comparativefixing device 7C2 with endurance of the image forming apparatus 1incorporating the fixing device 7 according to the first exemplaryembodiment. The endurance test uses a print chart having an image arearatio of 5 percent to print a toner image on one side of three sheetsrepeatedly to examine whether or not the fixing belt 20 suffers fromskew and breakage. In Table 1, k denotes 1,000 sheets.

TABLE 1 Configuration Skew and breakage of fixing belt 20 Comparativefixing device Breakage upon printing on 105k sheets 7C2 Fixing device 7No breakage upon printing on 200k sheets

As shown in Table 1, with the comparative fixing device 7C2, the fixingbelt 20 suffers from breakage upon printing on 105 k sheets. Conversely,with the fixing device 7 according to the first exemplary embodiment,the fixing belt 20 suffers from no breakage even upon printing on 200 ksheets. The result of the endurance test shows that the fixing device 7according to the first exemplary embodiment suppresses skew andresultant breakage of the fixing belt 20 more effectively than thecomparative fixing device 7C2.

A description is provided of various exemplary embodiments of fixingdevices other than the fixing device 7 according to the first exemplaryembodiment by explaining differences from the first exemplaryembodiment.

It is to be noted that the construction and the configuration of thefixing devices that are identical to those of the fixing device 7according to the first exemplary embodiment described above are omittedbecause the identical construction and configuration achieve similaroperation and advantages.

A description is provided of a construction of a fixing device 7Saccording to a second exemplary embodiment.

FIG. 7 is a schematic vertical sectional view of a main section of thefixing device 7S. As shown in FIG. 7, in addition to the fixing belt 20,the pressure roller 21, the fixing pad 22, the heating roller 23, thehalogen heater 24, and the fixing stay 26, the fixing device 7S includesa thermistor 48 and a thermostat 49 serving as a temperature detectorand a temperature detector holder 50 that holds the thermistor 48 andthe thermostat 49. The fixing device 7S does not include the platespring 25 serving as a tension applicator shown in FIG. 2. Instead, thefixing pad 22 and the heating roller 23 are fixed at positions where thefixing pad 22 is spaced apart from the heating roller 23 to exert apredetermined tension to the fixing belt 20. Thus, the fixing pad 22 andthe heating roller 23 serve as a tension applicator.

A detailed description is now given of a configuration of the thermistor48 and the thermostat 49.

The thermistor 48 is a temperature sensor that detects the temperatureof the fixing belt 20 to adjust the temperature of the fixing nip N. Thethermostat 49 connected to a power line connected to the halogen heater24 is a temperature sensor that interrupts power supply to the halogenheater 24 when the temperature of the fixing belt 20 increases to apredetermined temperature or higher. According to this exemplaryembodiment, the thermistor 48 does not contact the fixing belt 20.Alternatively, the thermistor 48 may contact the fixing belt 20.Further, a fuse may be used instead of the thermostat 49. The thermistor48 and the thermostat 49 may detect the temperature of the heatingroller 23.

A detailed description is now given of a construction of the temperaturedetector holder 50.

FIG. 8 is a perspective view of the temperature detector holder 50. Thetemperature detector holder 50 is manufactured by folding a rectangularplate on two parallel long edges thereof at a right angle. Thetemperature detector holder 50 includes a through-hole 50 a into which aprojection 48 a of the thermistor 48 is inserted; a screw hole 50 bthrough which a screw fastens the thermistor 48 to the temperaturedetector holder 50; a through-hole 50 c into which a body of thethermostat 49 is inserted; and a plurality of screw holes 50 d throughwhich a plurality of screws fastens the thermostat 49 to the temperaturedetector holder 50. The temperature detector holder 50 further includesa pair of heater holding portions 50 e that holds both lateral ends ofthe halogen heater 24 in a longitudinal direction thereof.

A description is provided of a construction of a holding mechanism and adriving force transmitter of the fixing device 7S.

FIG. 9 is a schematic vertical sectional view of the fixing device 7Sillustrating the holding mechanism and the driving force transmitter. Asshown in FIG. 9, the fixing device 7S includes a frame 41S including abelt support holder holding through-hole 41 bS that has a guide 41 cScontoured into an arch curved about the axis of the first gear 32.Accordingly, as a belt support holder 42S moves along the arcuate guide41 cS, the heating roller 23 and the heating roller gear 31 held by thebelt support holder 42S move arcuately. Since the heating roller gear 31moves arcuately about the axis of the first gear 32 meshing with theheating roller gear 31, a distance between the axis of the first gear 32and the axis of the heating roller gear 31 is constant.

According to the second exemplary embodiment, even when the belt supportholder 42S moves, the distance between the axis of the first gear 32 andthe axis of the heating roller gear 31 is constant, retaining precisemesh of the first gear 32 with the heating roller gear 31 and attainingstable transmission of the driving force from the first gear 32 to theheating roller gear 31.

Additionally, the temperature detector holder 50 moves together with thebelt support holder 42S. For example, the pressure lever 43 pressesagainst the temperature detector holder 50 to bring the temperaturedetector holder 50 into contact with the belt support holder 42S. As thebelt support holder 42S moves, the temperature detector holder 50 movesin accordance with motion of the belt support holder 42S while thetemperature detector holder 50 contacts the belt support holder 42S.

The temperature detector holder 50 moving together with the belt supportholder 42S retains a constant distance of the thermistor 48 and thethermostat 49 with respect to the heating roller 23 and the fixing belt20. Accordingly, the temperature detector holder 50 prevents degradationin accuracy in detecting the temperature of the fixing belt 20 which mayoccur as the distance between the temperature detector (e.g., thethermistor 48 and the thermostat 49) and a temperature detection object(e.g., the fixing belt 20) changes, attaining precise temperaturedetection by the temperature detector.

Additionally, the temperature detector holder 50 holding the halogenheater 24 retains a positional relation between the heating roller 23and the halogen heater 24. Accordingly, even if the heating roller 23has a decreased diameter, the temperature detector holder 50 preventsthe halogen heater 24 from coming into contact with the heating roller23.

A description is provided of a construction of a holding mechanism and adriving force transmitter of a fixing device 7T according to a thirdexemplary embodiment.

FIG. 10 is a schematic vertical sectional view of the fixing device 7Tillustrating the holding mechanism and the driving force transmitter. Asshown in FIG. 10, the fixing device 7T includes a frame 41T including abelt support holder holding through-hole 41 bT that has an arcuate guide41 g and a linear guide 41 h. The arcuate guide 41 g is contoured intoan arch curved about the axis of the first gear 32. The linear guide 41h extends linearly in a direction L in which a belt support holder 42Tmoves closer to and away from the pressure roller 21.

Additionally, the belt support holder 42T is constructed of twocomponents. A first component is a heating roller holding portion 42 dserving as a rotary belt support holding portion that holds the heatingroller 23 serving as a rotary belt support. A second component is afixing pad holding portion 42 e serving as an opposed belt supportholding portion that holds the fixing pad 22 serving as an opposed beltsupport.

FIG. 11 is a perspective view of the heating roller holding portion 42 dand the fixing pad holding portion 42 e before assembling. As shown inFIG. 11, the heating roller holding portion 42 d includes the heatingroller holding through-hole 42 b into which the axial end 23 a of theheating roller 23 is rotatably inserted and an engaging through-hole 42f to which the fixing pad holding portion 42 e is attached forassembling. The fixing pad holding portion 42 e includes an engagingprojection 42 g to be inserted into the engaging through-hole 42 f andthe fixing pad holding through-hole 42 a into which the fixing stay 26is inserted.

The heating roller holding portion 42 d further includes a slideprojection 42 h that slides over the arcuate guide 41 g depicted in FIG.10. The slide projection 42 h is concentric with the heating rollerholding through-hole 42 b. The fixing pad holding portion 42 e furtherincludes a pair of grooves 42 i to engage the linear guides 41 hdepicted in FIG. 10, respectively.

FIG. 12 is a sectional view of the heating roller holding portion 42 dand the fixing pad holding portion 42 e after assembling. The engagingprojection 42 g is inserted into the engaging through-hole 42 f toassemble the fixing pad holding portion 42 e to the heating rollerholding portion 42 d. Each of the engaging projection 42 g and theengaging through-hole 42 f is circular. The heating roller holdingportion 42 d and the fixing pad holding portion 42 e are relativelyrotatable about an axis of an outer circumference of the engagingprojection 42 g in a state in which the fixing pad holding portion 42 eis assembled to the heating roller holding portion 42 d. The heatingroller 23 held by the heating roller holding portion 42 d and the fixingpad 22 held by the fixing pad holding portion 42 e are behind theheating roller holding portion 42 d and the fixing pad holding portion42 e in FIG. 12.

A description is provided of movement of the heating roller holdingportion 42 d and the fixing pad holding portion 42 e.

FIG. 13A is a sectional view of the heating roller holding portion 42 dand the fixing pad holding portion 42 e before movement. FIG. 13B is asectional view of the heating roller holding portion 42 d and the fixingpad holding portion 42 e after movement.

As the heating roller holding portion 42 d and the fixing pad holdingportion 42 e move rightward in FIG. 13A, the slide projection 42 h ofthe heating roller holding portion 42 d moves arcuately along thearcuate guide 41 g in a direction K shown in FIG. 13B. Conversely, thefixing pad holding portion 42 e moves linearly along the linear guide 41h in the direction L shown in FIG. 13B. Thus, the slide projection 42 hof the heating roller holding portion 42 d draws a trajectory differentfrom that of the fixing pad holding portion 42 e. Accordingly, as theslide projection 42 h of the heating roller holding portion 42 d and thefixing pad holding portion 42 e move, a positional relation between theslide projection 42 h and the fixing pad holding portion 42 e changesvertically in FIG. 13B. However, the change in the positional relationis allowed or offset by rotation of the heating roller holding portion42 d about the engaging projection 42 g of the fixing pad holdingportion 42 e in a rotation direction S. Further, as the heating rollerholding portion 42 d rotates about the engaging projection 42 g, thepredetermined distance between the heating roller 23 and the fixing pad22 is retained.

As shown in FIG. 10, as the slide projection 42 h of the heating rollerholding portion 42 d moves arcuately, the heating roller 23 and theheating roller gear 31 held by the heating roller holding portion 42 dmove about the axis of the first gear 32 arcuately in the direction K.Accordingly, like in the second exemplary embodiment, even when the beltsupport holder 42T moves, the distance between the axis of the firstgear 32 and the axis of the heating roller gear 31 is constant,retaining precise mesh of the first gear 32 with the heating roller gear31 and attaining stable transmission of the driving force from the firstgear 32 to the heating roller gear 31.

Conversely, as the fixing pad holding portion 42 e moves linearly, thefixing pad 22 held by the fixing pad holding portion 42 e moves linearlyin a direction in which the fixing pad 22 moves closer to and away fromthe pressure roller 21 in the direction L. Thus, as the fixing pad 22moves linearly, the position and the direction of the fixing pad 22pressing against the pressure roller 21 do not change.

FIG. 14 is a graph showing a relation between the length of the fixingnip N in the sheet conveyance direction DP (hereinafter referred to asthe fixing nip length) and pressure exerted at the fixing nip N(hereinafter referred to as the fixing nip pressure) that changes as thebelt support holder 42S of the fixing device 7S according to the secondexemplary embodiment depicted in FIG. 9 and the belt support holder 42Tof the fixing device 7T according to the third exemplary embodimentdepicted in FIG. 10 move.

FIG. 14 illustrates a curve Cα in a dotted line indicating the relationbetween the fixing nip length and the fixing nip pressure of the fixingdevices 7S and 7T that use the pressure roller 21 before the endurancetest. FIG. 14 illustrates a curve Cβ in a long and short dashed line anda curve Cγ in a solid line indicating the relation between the fixingnip length and the fixing nip pressure of the fixing devices 7S and 7Tthat use the pressure roller 21 after the endurance test. The curve Cβindicates the relation between the fixing nip length and fixing nippressure of the fixing device 7S according to the second exemplaryembodiment. The curve Cγ indicates the relation between the fixing niplength and the fixing nip pressure of the fixing device 7T according tothe third exemplary embodiment. The pressure roller 21 after theendurance test has a decreased surface hardness and a decreased outerdiameter after performing a print job of printing on one side of threesheets with a print chart at an image area ratio of 5 percent repeatedlyuntil printing on 100 k sheets finishes.

As shown in FIG. 14, the curve Cα obtained with the pressure roller 21before the endurance test attains the identical relation between thefixing nip length and the fixing nip pressure with the fixing device 7Saccording to the second exemplary embodiment and the fixing device 7Taccording to the third exemplary embodiment. For example, a peak of thefixing nip pressure is at a middle of the fixing nip length. Conversely,the curve Cβ obtained with the fixing device 7S according to the secondexemplary embodiment using the pressure roller 21 after the endurancetest has a peak of the fixing nip pressure that is shifted from themiddle of the fixing nip length and a decreased fixing nip length. Thecurve Cγ obtained with the fixing device 7T according to the thirdexemplary embodiment using the pressure roller 21 after the endurancetest retains a peak of the fixing nip pressure that is at the middle ofthe fixing nip length and the fixing nip length that is equivalent tothe fixing nip length of the curve Cα.

It is presumed that the difference between the curves Cβ and Cγ iscaused by the difference in the direction in which the fixing pad 22moves between the fixing device 7S according to the second exemplaryembodiment and the fixing device 7T according to the third exemplaryembodiment. Since the pressure roller 21 after the endurance test has adecreased surface hardness, the pressure roller 21 may be deformedsubstantially by pressure from the fixing pad 22. Accordingly, thefixing pad 22 moves from an initial position before the endurance testtoward the pressure roller 21. In the fixing device 7S according to thesecond exemplary embodiment, the fixing pad 22 moves arcuately.Accordingly, the fixing pad 22 presses against the pressure roller 21 ata position shifted from a target pressurization position where thefixing pad 22 presses against the pressure roller 21 and therefore tiltsrelative to the pressure roller 21. Consequently, the curve Cβ has thepeak of the fixing nip pressure that is shifted from the middle of thefixing nip length and the decreased fixing nip length. Conversely, thefixing pad 22 of the fixing device 7T according to the third exemplaryembodiment moves linearly, suppressing change in the position and thedirection of the fixing pad 22 pressing against the pressure roller 21.Consequently, the curve Cγ does not have the peak of the fixing nippressure that is shifted from the middle of the fixing nip length andthe decreased fixing nip length.

As described above, with the fixing device 7T according to the thirdexemplary embodiment, even if the fixing pad 22 moves, the fixing device7T attains the curve Cγ that retains the peak of the fixing nip pressureand the fixing nip length that are equivalent to those of the curve Cα.Hence, the fixing device 7T according to the third exemplary embodimentattains a desired fixing property of fixing the toner image T on thesheet P properly and a desired separation property of separating thesheet P from the fixing belt 20 precisely.

A description is provided of a construction of a holding mechanism and adriving force transmitter of a fixing device 7U according to a fourthexemplary embodiment.

FIG. 15 is a schematic vertical sectional view of the fixing device 7Uillustrating the holding mechanism and the driving force transmitter. Asshown in FIG. 15, the fixing device 7U includes a gear holder 52pivotably mounted on the second gear 33 to hold the first gear 32 suchthat the first gear 32 is movable arcuately in a direction M about anaxis of the second gear 33.

A pressure spring 53 serving as a biasing member presses against thegear holder 52 upward in FIG. 15 toward the heating roller gear 31.Thus, the pressure spring 53 biases the first gear 32 against theheating roller gear 31. The pressure spring 53 biases the gear holder 52against a belt support holder 42U, bringing the gear holder 52 intocontact with the belt support holder 42U. The gear holder 52 includes anarcuate restrictor 52 a. The belt support holder 42U includes an arcuaterestrictor 42 j that contacts the restrictor 52 a of the gear holder 52.The restrictor 52 a of the gear holder 52 is contoured into an archcurved about the axis of the first gear 32. The restrictor 42 j of thebelt support holder 42U is contoured into an arch curved about the axisof the heating roller gear 31.

Accordingly, as the belt support holder 42U moves linearly with respectto the pressure roller 21 in a direction in which the belt supportholder 42U moves closer to and away from the pressure roller 21, thefirst gear 32 moves in accordance with motion of the heating roller gear31 by a bias from the pressure spring 53. Since the first gear 32 movesarcuately about the axis of the second gear 33, a distance between theaxis of the first gear 32 and the axis of the second gear 33 isconstant, retaining precise mesh between the first gear 32 and thesecond gear 33.

The restrictor 52 a of the gear holder 52 contacting the restrictor 42 jof the belt support holder 42U prohibits the first gear 32 from movingcloser to the heating roller gear 31 for a predetermined distance ormore. Accordingly, even if the heating roller gear 31 moves, thedistance between the axis of the first gear 32 and the axis of theheating roller gear 31 is constant. Thus, the first gear 32 meshes withthe heating roller gear 31 precisely.

According to the fourth exemplary embodiment, even when the belt supportholder 42U moves linearly, mesh between the heating roller gear 31 andthe first gear 32 and mesh between the first gear 32 and the second gear33 are retained precisely, attaining stable transmission of the drivingforce. Additionally, the fixing pad 22 moves linearly relative to thepressure roller 21, retaining the peak of the fixing nip pressure andthe desired fixing nip length and therefore attaining the desired fixingproperty of fixing the toner image T on the sheet P properly and thedesired separation property of separating the sheet P from the fixingbelt 20 precisely.

A description is provided of a construction of a holding mechanism and adriving force transmitter of a fixing device 7V according to a fifthexemplary embodiment.

FIG. 16 is a schematic vertical sectional view of the fixing device 7Villustrating the holding mechanism and the driving force transmitter. Asshown in FIG. 16, the fixing device 7V according to the fifth exemplaryembodiment is different from the fixing device 7U according to thefourth exemplary embodiment in the arrangement of a plurality of gears.For example, the first gear 32 and the second gear 33 are disposed abovethe heating roller gear 31 in FIG. 16. The fixing device 7V includes athird gear 34 that meshes with the driving gear located inside the imageforming apparatus 1. A driving force from the driving gear istransmitted to the pressure roller gear 30 through the third gear 34.The driving force is further transmitted from the pressure roller gear30 to the heating roller gear 31 through the second gear 33 and thefirst gear 32.

Like the first gear 32 of the fixing device 7U according to the fourthexemplary embodiment shown in FIG. 15, the first gear 32 of the fixingdevice 7V according to the fifth exemplary embodiment is held by thegear holder 52 such that the first gear 32 is movable arcuately in thedirection M about the axis of the second gear 33 in accordance withmotion of the heating roller gear 31. However, unlike the fixing device7U according to the fourth exemplary embodiment, the fixing device 7Vaccording to the fifth exemplary embodiment does not incorporate thepressure spring 53 that biases the first gear 32 against a belt supportholder 42V. Instead of a bias from the pressure spring 53, a weight ofthe first gear 32 and the gear holder 52 and a bias exerted between thefirst gear 32 and the heating roller gear 31 while the first gear 32 andthe heating roller gear 31 are driven and rotated bias the first gear 32against the heating roller gear 31.

FIG. 17 is a schematic vertical sectional view of the fixing device 7Villustrating the third gear 34, the pressure roller gear 30, the secondgear 33, the first gear 32, and the heating roller gear 31. As shown inFIG. 17, as the third gear 34, the pressure roller gear 30, the secondgear 33, the first gear 32, and the heating roller gear 31 rotate inrotation directions D34, D30, D33, D32, and D31, respectively, theheating roller gear 31 receives a driving force F from the first gear32. Conversely, the first gear 32 receives a reaction force R directedin a direction opposite a direction of the driving force F. The reactionforce R is directed in the direction inclined by a pressure angle α froma perpendicular line Q3 perpendicular to a linear line Q1 defined by theaxis of the heating roller gear 31 and the axis of the first gear 32.According to this exemplary embodiment, the reaction force R is directedobliquely downward in FIG. 17. The reaction force R has a component r1directed in a direction in which the first gear 32 moves toward theheating roller gear 31. The component r1 biases the first gear 32against the heating roller gear 31.

The component r1 of the reaction force R biasing the first gear 32against the heating roller gear 31 satisfies a following formula (1).

−90°−α≦θ≦90°−α  (1)

In the formula (1), θ represents an angle defined by the linear line Q1defined by the axis of the heating roller gear 31 and the axis of thefirst gear 32 and a linear line Q2 defined by the axis of the first gear32 and the axis of the second gear 33 in the rotation direction D32 ofthe first gear 32 rotating clockwise in FIG. 17. For example, if thepressure angle α is 20 degrees, the angle θ is defined by a formula (2)below.

−110°≦θ≦70°  (2)

FIG. 18 is a schematic vertical sectional view of the fixing device 7Uillustrating the pressure roller gear 30, the second gear 33, the firstgear 32, and the heating roller gear 31. As shown in FIG. 18illustrating the arrangement of the plurality of gears of the fixingdevice 7U according to the fourth exemplary embodiment, the angle θ is300 degrees. Accordingly, if the pressure angle α is 20 degrees, theangle θ does not satisfy the formula (2) above. Consequently, the fixingdevice 7U according to the fourth exemplary embodiment does not attain abias that biases the first gear 32 against the heating roller gear 31 bythe driving force transmitted to the heating roller gear 31 from thefirst gear 32.

As described above, with the fixing device 7V according to the fifthexemplary embodiment shown in FIGS. 16 and 17, the weight of the firstgear 32 and the gear holder 52 and the bias exerted between the firstgear 32 and the heating roller gear 31 while the first gear 32 and theheating roller gear 31 are driven and rotated bias the first gear 32against the heating roller gear 31. Accordingly, the fixing device 7Vdoes not incorporate the biasing member that biases the first gear 32against the heating roller gear 31, simplifying the construction of thefixing device 7V and reducing manufacturing costs.

The present disclosure is not limited to the details of the exemplaryembodiments described above and various modifications and improvementsare possible. The holding mechanism and the driving force transmitterincorporated in the fixing devices 7, 7S, 7T, 7U, and 7V are alsoapplicable to a belt device that incorporates an endless belt.

A description is provided of operation and advantages of variousconfigurations 1 to 15 of a belt device 7B and the fixing devices 7, 7S,7T, 7U, and 7V.

It is to be noted that the belt device 7B defined below is installablein the fixing devices 7, 7S, 7T, 7U, and 7V.

A configuration 1 is defined by the belt device 7B shown in FIGS. 2 and3. As shown in FIG. 3, the belt device 7B includes an endless belt(e.g., the fixing belt 20), a rotary driver (e.g., the pressure roller21), an opposed belt support (e.g., the fixing pad 22), a rotary beltsupport (e.g., the heating roller 23), a tension applicator (e.g., theplate spring 25), a belt support holder (e.g., the belt support holder42), and a biasing assembly (e.g., the pressure lever 43 and thepressure spring 44). The rotary driver contacts an outer circumferentialsurface of the belt to drive and rotate the belt. The opposed beltsupport is disposed opposite the rotary driver and in contact with aninner circumferential surface of the belt. The rotary belt support isdisposed opposite the rotary driver via the opposed belt support and incontact with the inner circumferential surface of the belt. The tensionapplicator exerts tension to the belt. The belt support holder holds theopposed belt support and the rotary belt support to retain apredetermined interval between the opposed belt support and the rotarybelt support. The biasing assembly presses against the belt supportholder to move the opposed belt support and the rotary belt supportcollectively with respect to the rotary driver in a direction in whichthe opposed belt support and the rotary belt support move closer to andaway from the rotary driver and to bias the opposed belt support againstthe rotary driver.

According to the configuration 1, the opposed belt support and therotary belt support move collectively in the direction in which theopposed belt support and the rotary belt support move closer to and awayfrom the rotary driver while retaining the predetermined intervalbetween the opposed belt support and the rotary belt support, thuspreventing change in tension exerted to the belt. Accordingly, the beltdevice 7B prevents increase in tension exerted to the belt, which mayincrease a driving torque. The belt device 7B also prevents decrease intension exerted to the belt, which may skew the belt.

A configuration 2 is defined by the configuration 1 in which one lateralend of the rotary belt support in an axial direction thereof receives adriving force and the belt support holder receives a bias that generatesat the one lateral end of the rotary belt support in the axial directionthereof as it is exerted with the driving force.

According to the configuration 2, the belt support holder, as itreceives the bias generated at the one lateral end of the rotary beltsupport in the axial direction thereof, prevents the bias from changingthe tension exerted to the belt. Accordingly, the belt support holderprevents variation in the tension exerted to the belt between onelateral end and another lateral end of the belt in an axial directionthereof and thereby prevents skew of the belt that results fromvariation in the tension exerted to the belt.

A configuration 3 is defined by the configuration 2 in which the rotarybelt support mounts a rotary belt support gear (e.g., the heating rollergear 31) at the one lateral end of the rotary belt support in the axialdirection thereof. The rotary belt support gear meshes with a first gear(e.g., the first gear 32) so that the driving force is transmitted tothe rotary belt support through the first gear and the rotary beltsupport gear. As shown in FIGS. 9 and 10, the belt support holder (e.g.,the belt support holders 42S and 42T) moves arcuately about an axis ofthe first gear.

According to the configuration 3, the belt support holder that movesarcuately about the axis of the first gear, even when the belt supportholder moves, retains a constant distance between the axis of the firstgear and an axis of the rotary belt support gear. Accordingly, the firstgear meshes with the rotary belt support gear precisely, attainingstable transmission of the driving force from the first gear to therotary belt support gear.

A configuration 4 shown in FIG. 10 is defined by the configuration 3 inwhich the belt support holder includes a rotary belt support holdingportion (e.g., the heating roller holding portion 42 d) that holds therotary belt support and an opposed belt support holding portion (e.g.,the fixing pad holding portion 42 e) that holds the opposed beltsupport. The rotary belt support holding portion moves arcuately aboutthe axis of the first gear. The opposed belt support holding portionmoves linearly with respect to the rotary driver in the direction L inwhich the opposed belt support holding portion moves closer to and awayfrom the rotary driver.

According to the configuration 4, the rotary belt support holdingportion that moves arcuately about the axis of the first gear, even whenthe rotary belt support holding portion moves, retains the constantdistance between the axis of the first gear and the axis of the rotarybelt support gear. Accordingly, the first gear meshes with the rotarybelt support gear precisely, attaining stable transmission of thedriving force from the first gear to the rotary belt support gear.Conversely, the opposed belt support holding portion moves linearly withrespect to the rotary driver in the direction L in which the opposedbelt support holding portion moves closer to and away from the rotarydriver, suppressing change in the position and the direction of theopposed belt support with respect to the rotary driver.

A configuration 5 shown in FIG. 10 is defined by the configuration 4 inwhich the belt device further includes an arcuate guide (e.g., thearcuate guide 41 g) and a linear guide (e.g., the linear guide 41 h).The arcuate guide guides the rotary belt support holding portionarcuately about the axis of the first gear. The linear guide guides theopposed belt support holding portion linearly in the direction L inwhich the opposed belt support holding portion moves closer to and awayfrom the rotary driver. As shown in FIGS. 13A and 13B, the rotary beltsupport holding portion is assembled with the opposed belt supportholding portion such that the rotary belt support holding portion isrotatable relative to the opposed belt support holding portion.

According to the configuration 5, the rotary belt support holdingportion that is rotatable relative to the opposed belt support holdingportion allows the rotary belt support holding portion and the opposedbelt support holding portion to move on the different trajectories,respectively.

A configuration 6 shown in FIG. 15 is defined by the configuration 2 inwhich the belt support holder (e.g., the belt support holder 42U) moveslinearly in the direction D in which the belt support holder movescloser to and away from the rotary driver. The rotary belt supportmounts the rotary belt support gear at the one lateral end of the rotarybelt support in the axial direction thereof. The rotary belt supportgear meshes with the first gear that meshes with a second gear (e.g.,the second gear 33) so that the driving force is transmitted to therotary belt support through the second gear, the first gear, and therotary belt support gear. The first gear moves arcuately about an axisof the second gear in accordance with motion of the belt support holder.

According to the configuration 6, since the first gear moves arcuatelyabout the axis of the second gear, a distance between the axis of thefirst gear and the axis of the second gear is constant, retainingprecise mesh between the first gear and the second gear. Further, thefirst gear that moves in accordance with motion of the belt supportholder retains mesh with the rotary belt support gear. Accordingly, thefirst gear meshes with the rotary belt support gear precisely, attainingstable transmission of the driving force from the first gear to therotary belt support gear.

A configuration 7 shown in FIG. 15 is defined by the configuration 6 inwhich the belt device further includes a biasing member (e.g., thepressure spring 53) that biases the first gear against the rotary beltsupport gear.

According to the configuration 7, a bias from the biasing member retainsprecise mesh between the first gear and the rotary belt support gear.

A configuration 8 shown in FIG. 17 is defined by the configuration 6 inwhich a following relation is satisfied:

−90°−α≦θ≦90°−α

where θ represents an angle defined by the linear line Q1 defined by theaxis of the rotary belt support gear and the axis of the first gear andthe linear line Q2 defined by the axis of the first gear and the axis ofthe second gear in the rotation direction D32 of the first gear; αrepresents a pressure angle of the driving force transmitted from thefirst gear to the rotary belt support gear.

According to the configuration 8, the angle θ and the pressure angle αthat satisfy the above relation generate a bias that biases the firstgear against the rotary belt support gear as the driving force istransmitted to the rotary belt support gear. Accordingly, the biasretains precise mesh between the first gear and the rotary belt supportgear.

A configuration 9 shown in FIG. 15 is defined by any one of theconfigurations 6 to 8 in which the belt device further includes a gearholder (e.g., the gear holder 52) that holds the first gear and has afirst restrictor (e.g., the restrictor 52 a). The belt support holder(e.g., the belt support holder 42U) includes a second restrictor (e.g.,the restrictor 42 j) that contacts the first restrictor to restrictmotion of the first gear that moves closer to the rotary belt supportgear so as to retain the constant distance between the axis of therotary belt support gear and the axis of the first gear.

According to the configuration 9, the first restrictor and the secondrestrictor restrict motion of the first gear that moves closer to therotary belt support gear, retaining the constant distance between theaxis of the rotary belt support gear and the axis of the first gear.Accordingly, the first gear meshes with the rotary belt support gearprecisely, attaining stable transmission of the driving force from thefirst gear to the rotary belt support gear.

A configuration 10 shown in FIG. 7 is defined by any one of theconfigurations 1 to 9 in which a fixing device (e.g., the fixing devices7, 7S, 7T, 7U, and 7V) includes a temperature detector (e.g., thethermistor 48 and the thermostat 49) disposed opposite at least one ofthe belt and the rotary belt support to detect the temperature of the atleast one of the belt and the rotary belt support and a temperaturedetector holder (e.g., the temperature detector holder 50) that holdsthe temperature detector. As shown in FIG. 9, the biasing assemblypresses the temperature detector holder against the belt support holderto move the temperature detector holder together with the belt supportholder while retaining an interval between the temperature detector andthe rotary belt support.

According to the configuration 10, the temperature detector holdermoving together with the belt support holder retains a constant distancebetween the temperature detector and the rotary belt support.Accordingly, the temperature detector holder prevents degradation inaccuracy in detecting the temperature of a temperature detection object(e.g., the fixing belt 20 and the heating roller 23) which may occur asthe distance between the temperature detector and the temperaturedetection object changes, attaining precise temperature detection by thetemperature detector.

A configuration 11 shown in FIGS. 2 and 8 is defined by theconfiguration 10 in which the fixing device incorporating the beltdevice includes a heater (e.g., the halogen heater 24) to heat the beltthrough the rotary belt support. As shown in FIG. 8, the temperaturedetector holder includes a heater holding portion (e.g., the heaterholding portion 50 e) that holds the heater.

According to the configuration 11, the temperature detector holder thatholds the heater allows the heater to move together with the temperaturedetector holder as the temperature detector holder moves together withthe belt support holder. Accordingly, the heater retains a positionalrelation with the rotary belt support, the opposed belt support, and thebelt and therefore is immune from accidental contact with the rotarybelt support, the opposed belt support, and the belt.

A configuration 12 shown in FIG. 3 is defined by any one of theconfigurations 1 to 11 in which the belt support holder includes abiasing assembly side end (e.g., the pressure lever side end 42 m) thatis opposite a rotary driver side end (e.g., the pressure roller side end42 n) disposed opposite the rotary driver and is pressed by the biasingassembly toward the rotary driver. The belt support holder furtherincludes a rotary belt support holding through-hole (e.g., the heatingroller holding through-hole 42 b) having the length E1 in apressurization direction of the biasing assembly. The rotary beltsupport includes an axial end (e.g., the axial end 23 a) disposed at onelateral end of the rotary belt support in the axial direction thereofand rotatably inserted into the rotary belt support holdingthrough-hole. The length E1 of the rotary belt support holdingthrough-hole is greater than the length E2 of the axial end of therotary belt support in the pressurization direction of the biasingassembly.

According to the configuration 12, even if the rotary belt supportholding through-hole, since it has the length E1 defined above, isdeformed as the belt support holder receives pressure from the biasingassembly, the rotary belt support holding through-hole retains smoothrotation of the rotary belt support, preventing increase of the rotationtorque of the rotary belt support.

A configuration 13 is defined by any one of the configurations 1 to 12in which the belt support holder is disposed at each lateral end of therotary belt support in the axial direction thereof. Each belt supportholder is constructed of identical parts.

Each belt support holder constructed of the identical parts reducesvariation in a positional relation between the rotary belt support andthe opposed belt support at one lateral end and another lateral end ofthe belt in the axial direction thereof. Accordingly, the belt supportholder suppresses variation in tension exerted to the belt that resultsfrom variation in the positional relation between the rotary beltsupport and the opposed belt support in the axial direction of the belt,thus suppressing skew of the belt.

A configuration 14 shown in FIG. 2 is defined by any one of theconfigurations 1 to 13 in which the belt device is incorporated in thefixing device (e.g., the fixing devices 7, 7S, 7T, 7U, and 7V) thatfixes the toner image T on the sheet P serving as a recording medium asthe sheet P bearing the toner image T is conveyed through the fixing nipN formed between the belt and the rotary driver.

A configuration 15 shown in FIG. 1 is defined by an image formingapparatus (e.g., the image forming apparatus 1) that includes the fixingdevice according to the configuration 14.

According to the exemplary embodiments described above, the fixing belt20 serves as an endless belt. Alternatively, a fixing film, a fixingsleeve, or the like may be used as an endless belt. Further, thepressure roller 21 serves as a rotary driver. Alternatively, a pressurebelt or the like may be used as a rotary driver.

The present disclosure has been described above with reference tospecific exemplary embodiments. Note that the present disclosure is notlimited to the details of the embodiments described above, but variousmodifications and enhancements are possible without departing from thespirit and scope of the disclosure. It is therefore to be understoodthat the present disclosure may be practiced otherwise than asspecifically described herein. For example, elements and/or features ofdifferent illustrative exemplary embodiments may be combined with eachother and/or substituted for each other within the scope of the presentdisclosure.

What is claimed is:
 1. A belt device comprising: an endless belt; arotary driver contacting an outer circumferential surface of the belt todrive and rotate the belt; an opposed belt support disposed opposite therotary driver and in contact with an inner circumferential surface ofthe belt; a rotary belt support disposed opposite the rotary driver viathe opposed belt support and in contact with the inner circumferentialsurface of the belt; a belt support holder to hold the opposed beltsupport and the rotary belt support to retain a predetermined intervalbetween the opposed belt support and the rotary belt support; and abiasing assembly to press against the belt support holder to move theopposed belt support and the rotary belt support collectively withrespect to the rotary driver and bias the opposed belt support againstthe rotary driver.
 2. The belt device according to claim 1, furthercomprising a tension applicator to exert tension to the belt.
 3. Thebelt device according to claim 1, further comprising a rotary beltsupport gear mounted on one lateral end of the rotary belt support in anaxial direction thereof to transmit a driving force to the rotary beltsupport, wherein the belt support holder receives a bias generated atthe one lateral end of the rotary belt support in the axial directionthereof by the driving force.
 4. The belt device according to claim 3,further comprising a first gear to mesh with the rotary belt supportgear to transmit the driving force to the rotary belt support gear. 5.The belt device according to claim 4, wherein the belt support holdermoves arcuately about an axis of the first gear.
 6. The belt deviceaccording to claim 5, wherein the belt support holder includes: a rotarybelt support holding portion to hold the rotary belt support and movearcuately about the axis of the first gear; and an opposed belt supportholding portion to hold the opposed belt support and move linearly withrespect to the rotary driver.
 7. The belt device according to claim 6,further comprising: an arcuate guide to guide the rotary belt supportholding portion arcuately about the axis of the first gear; and a linearguide to guide the opposed belt support holding portion linearly withrespect to the rotary driver, wherein the rotary belt support holdingportion is assembled with the opposed belt support holding portion suchthat the rotary belt support holding portion is rotatable relative tothe opposed belt support holding portion.
 8. The belt device accordingto claim 7, wherein the rotary belt support holding portion includes aslide projection to slide over the arcuate guide, and wherein theopposed belt support holding portion includes a groove to engage thelinear guide.
 9. The belt device according to claim 4, furthercomprising a second gear to mesh with the first gear to transmit thedriving force to the first gear, wherein the belt support holder moveslinearly with respect to the rotary driver, and wherein the first gearmoves arcuately about an axis of the second gear in accordance withmotion of the belt support holder.
 10. The belt device according toclaim 9, further comprising a biasing member to bias the first gearagainst the rotary belt support gear.
 11. The belt device according toclaim 9, wherein a following relation is satisfied:−90°−α≦θ≦90°−α where θ represents an angle defined by a linear linedefined by an axis of the rotary belt support gear and an axis of thefirst gear and a linear line defined by the axis of the first gear andthe axis of the second gear in a rotation direction of the first gearand α represents a pressure angle of the driving force transmitted fromthe first gear to the rotary belt support gear.
 12. The belt deviceaccording to claim 9, further comprising a first restrictor connected tothe first gear, wherein the belt support holder includes a secondrestrictor contacting the first restrictor to restrict motion of thefirst gear that moves toward the rotary belt support gear so as toretain a constant distance between an axis of the rotary belt supportgear and an axis of the first gear.
 13. The belt device according toclaim 12, further comprising a gear holder, provided with the firstrestrictor, to hold the first gear.
 14. The belt device according toclaim 1, wherein the belt support holder is disposed at each lateral endof the rotary belt support in an axial direction thereof.
 15. The beltdevice according to claim 14, wherein the belt support holder includes:a rotary driver side end disposed opposite the rotary driver; a biasingassembly side end that is opposite the rotary driver side end andpressed by the biasing assembly toward the rotary driver; and a rotarybelt support holding through-hole having a length in a pressurizationdirection of the biasing assembly, wherein the rotary belt supportincludes an axial end disposed at each lateral end of the rotary beltsupport in the axial direction thereof and rotatably inserted into therotary belt support holding through-hole, and wherein the length of therotary belt support holding through-hole is greater than a length of theaxial end of the rotary belt support in the pressurization direction ofthe biasing assembly.
 16. The belt device according to claim 15, furthercomprising an opposed belt support holder to hold the opposed beltsupport, wherein the belt support holder further includes an opposedbelt support holding through-hole into which the opposed belt supportholder is inserted.
 17. A fixing device comprising: an endless belt; aheater to heat the belt; a rotary driver contacting an outercircumferential surface of the belt to drive and rotate the belt; anopposed belt support disposed opposite the rotary driver and in contactwith an inner circumferential surface of the belt; a rotary belt supportdisposed opposite the rotary driver via the opposed belt support and incontact with the inner circumferential surface of the belt; a beltsupport holder to hold the opposed belt support and the rotary beltsupport to retain a predetermined interval between the opposed beltsupport and the rotary belt support; and a biasing assembly to pressagainst the belt support holder to move the opposed belt support and therotary belt support collectively with respect to the rotary driver andbias the opposed belt support against the rotary driver.
 18. The fixingdevice according to claim 17, further comprising: a temperature detectordisposed opposite at least one of the belt and the rotary belt supportto detect a temperature of the at least one of the belt and the rotarybelt support; and a temperature detector holder to hold the temperaturedetector, wherein the biasing assembly presses the temperature detectorholder against the belt support holder to move the temperature detectorholder together with the belt support holder while retaining an intervalbetween the temperature detector and the rotary belt support.
 19. Thefixing device according to claim 18, wherein the temperature detectorholder includes a heater holding portion to hold the heater.
 20. Animage forming apparatus comprising: an image forming device to form atoner image; and a fixing device disposed downstream from the imageforming device in a recording medium conveyance direction to fix thetoner image on a recording medium, the fixing device including: anendless belt; a heater to heat the belt; a rotary driver contacting anouter circumferential surface of the belt to drive and rotate the belt;an opposed belt support disposed opposite the rotary driver and incontact with an inner circumferential surface of the belt; a rotary beltsupport disposed opposite the rotary driver via the opposed belt supportand in contact with the inner circumferential surface of the belt; abelt support holder to hold the opposed belt support and the rotary beltsupport to retain a predetermined interval between the opposed beltsupport and the rotary belt support; and a biasing assembly to pressagainst the belt support holder to move the opposed belt support and therotary belt support collectively with respect to the rotary driver andbias the opposed belt support against the rotary driver.